U.S. patent application number 11/094509 was filed with the patent office on 2005-10-13 for head driving device.
This patent application is currently assigned to SEIKO EPSON CORPORATION. Invention is credited to Umeda, Atsushi.
Application Number | 20050225579 11/094509 |
Document ID | / |
Family ID | 35060110 |
Filed Date | 2005-10-13 |
United States Patent
Application |
20050225579 |
Kind Code |
A1 |
Umeda, Atsushi |
October 13, 2005 |
Head driving device
Abstract
A head driving device of a liquid ejecting apparatus includes a
pressure generating element, a bias voltage applying unit which
applies a bias voltage to the pressure generating element, a
driving voltage generating unit which generates and outputs a
driving voltage to the pressure generating element for ejecting a
liquid droplet from a nozzle of a liquid ejecting head, and a
cutoff unit which cuts off the bias voltage applied to the pressure
generating element based on an outputting of a drive stopping
signal.
Inventors: |
Umeda, Atsushi; (Nagano,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SEIKO EPSON CORPORATION
|
Family ID: |
35060110 |
Appl. No.: |
11/094509 |
Filed: |
March 31, 2005 |
Current U.S.
Class: |
347/9 |
Current CPC
Class: |
B41J 2/04541 20130101;
B41J 2/04581 20130101 |
Class at
Publication: |
347/009 |
International
Class: |
B41J 029/38 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2004 |
JP |
P2004-102921 |
Mar 31, 2004 |
JP |
P2004-101740 |
Mar 14, 2005 |
JP |
P2005-071332 |
Mar 14, 2005 |
JP |
P2005-071333 |
Claims
What is claimed is:
1. A head driving device of a liquid ejecting apparatus,
comprising: a pressure generating element; a bias voltage applying
unit which applies a bias voltage to the pressure generating
element; a driving voltage generating unit which generates and
outputs a driving voltage to the pressure generating element for
ejecting a liquid droplet from a nozzle of a liquid ejecting head;
and a cutoff unit which cuts off the bias voltage applied to the
pressure generating element based on a drive stopping signal.
2. The head driving device as set forth in claim 1, wherein the
bias voltage applying unit is supplied with a power from a first
power source for charging, and wherein a voltage of the first power
source is lower than a voltage of a second power source for
supplying a power to the driving voltage generating unit for
charging.
3. The head driving device as set forth in claim 1, wherein the
cutoff unit forms a circuit for discharging a charge which is
charged on the bias voltage applying unit when the drive stopping
signal is outputted.
4. The head driving device as set forth in claim 1, wherein the
cutoff unit forms a circuit for charging the bias voltage applying
unit by supplying the power from the first power source to the bias
voltage applying unit when the drive stopping signal is not
outputted.
5. The head driving device as set forth in claim 1, wherein the
cutoff unit forms a circuit for charging the bias voltage applying
unit by supplying the power from the second power source to the
bias voltage applying unit when the drive stopping signal is not
outputted.
6. The head driving device as set forth in claim 4, wherein the
circuit is formed based on a drive instruction signal which is
outputted when the liquid ejecting head restarts a liquid ejecting
operation from a standby state.
7. The head driving device as set forth in claim 5, wherein the
circuit is formed based on a drive instruction signal which is
outputted when the liquid ejecting head restarts a liquid ejecting
operation from a standby state.
8. A head driving device of a liquid ejecting apparatus,
comprising: a pressure generating element; a bias voltage applying
unit which applies a bias voltage to the pressure generating
element; a driving voltage generating unit which generates and
outputs a driving voltage to the pressure generating element for
ejecting a liquid droplet from a nozzle of a liquid ejecting head;
a first charging unit which charges the bias voltage applying unit
at a first voltage; and a second charging unit which charges the
bias voltage applying unit at a second voltage greater than the
first voltage when a drive instruction signal is outputted to the a
driving voltage generating unit.
9. The head driving device as set forth in claim 8, wherein the
second voltage is a voltage outputted from the driving voltage
generating unit.
10. The head driving device as set forth in claim 8, wherein the
drive instruction signal is a signal outputted when the liquid
ejecting head restarts a liquid ejecting operation from a standby
state.
11. The head driving device as set forth in claim 8, wherein the
second charging unit charges the bias voltage applying unit at a
first charge time period shorter than a second charge time period
for charging the bias voltage applying unit by the first charging
unit.
12. The head driving device as set forth in claim 8, further
comprising a cutoff unit which cuts off the bias voltage applied to
the pressure generating element when a drive stopping signal is
outputted to the driving voltage generating unit.
13. A method of cutting off an applied voltage to a pressure
generating element of a head driving device of a liquid ejecting
apparatus, comprising: applying a bias voltage to the pressure
generating element; generating and outputting a driving voltage to
the pressure generating element for ejecting a liquid droplet from
a nozzle; and cutting-off the bias voltage applied to the pressure
generating element based on a drive stopping signal.
14. A method of charging a bias voltage applying unit for applying
a bias voltage to a pressure generating element of a head driving
device of a liquid ejecting apparatus, comprising: applying a bias
voltage to the pressure generating element; generating and
outputting a driving voltage to the pressure generating element for
ejecting a liquid droplet from a nozzle of a liquid ejecting head;
charging the bias voltage applying unit at a first voltage; and
charging the bias voltage applying unit at a second voltage greater
than the first voltage when a drive instruction signal is outputted
to the a driving voltage generating unit.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a head driving device for
driving various portions of a liquid ejecting head.
[0002] In a related art, there is proposed a circuit for driving a
printing head with an object of enabling to eject ink stably from a
nozzle opening even when a number of pressure generating elements
(for example, piezoelectric elements) to be driven is varied. The
related printing head driving circuit applies a predetermined
potential (correcting potential) from a first switching speed
correcting circuit and a second switching speed correcting circuit
to a base of a transistor at a post stage of transistors connected
in Derlington connection in a drive signal outputting circuit via a
terminal for applying the correcting potential, thereby, it is
possible to execute assisting injection of charge to the base of
the transistor at the post stage or assisting flow out of charge
from the base. As a result, a switching speed of the transistor of
the post stage can arbitrarily be corrected in accordance with the
potential applied to the terminal for applying the collecting
potential (refer to, for example, JP-A-2000-211126).
[0003] Meanwhile, according to a related printing head driving
circuit shown in FIG. 7, by making a potential of a drive voltage
transmitting line 11 for connecting a power amplifying circuit 3
and an analog switch 7 or the like on a side of a printing head 5
(hereinafter, described as "COM potential") coincide with a bias
potential of a piezoelectric element 9 when printing is stopped,
stability of printing is increased and service life of the
piezoelectric element 9 is also prolonged. However, an output
voltage from a direct current power source of 42V is applied to a
side of a drive voltage generating circuit 1 including the power
amplifying circuit 3 as a drive power source. Also, charge charged
from a direct current power source of 5V to a capacitor 15 via a
resistor 13 is applied to the side of the piezoelectric element 9
as the bias voltage of the piezoelectric element 9. Therefore, a
potential difference is produced between the COM potential and the
bias potential of the piezoelectric element 9. As a result, a leak
current is made to flow to the piezoelectric element 9 through the
drive voltage transmitting line 11. Therefore, there poses a
problem that a power consumption amount of the printer at standby
state is considerable.
[0004] Further, in the related printing head driving circuit shown
in FIG. 7, a capacitance of an (electrolytic) capacitor 15 for
applying a bias voltage to respective piezoelectric elements 9 is
far larger than a capacitance of a plurality of pieces of the
piezoelectric elements 9 (in FIG. 7, only one piece of the
piezoelectric element designated by numeral 9 is illustrated for
convenience of illustration and explanation) provided at respective
nozzles. This is because whereas a piezoelectric element having a
small capacitance equal to or smaller than, for example, 1 .mu.F is
used for each of the piezoelectric elements 9, an (electrolytic)
capacitor having a large capacity of about, for example, 4000 .mu.F
is used for the (electrolytic) capacitor 15.
[0005] The reason of using the (electrolytic) capacitor having the
capacitance far larger than the capacitance of the piezoelectric
elements 9 in this way as the capacitor 15 is that a voltage
charged to the capacitor 15 through a resistor 13 (of, for example,
400.mu..OMEGA.) from a direct current power source (of, for
example, 5V) is applied from the capacitor 15 to the respective
piezoelectric elements 9 as the bias voltage. In other words, since
the capacitor 15 achieves a function as a storage battery, the
capacitor having the large capacitance needs to use as the
capacitor 15. Therefore, a time constant (CR) determined by a
product of the capacitance (4000 .mu.F) of the capacitor 15 by a
resistance value (4000.mu..OMEGA.) of the resistor 13 is large and
therefore, time is taken for charging the capacitor 15 until an
output voltage from the capacitor 15 reaches the above-described
power source voltage (for example, 5V) (for example, about several
second are required).
[0006] The printing head driving circuit illustrated in FIG. 7 does
not pose a serious problem even when time is taken in charging the
above-described capacitor 15 from the above described direct
current power source, in the case in which the drive power source
is temporarily made OFF to stop printing operation of the printer
and thereafter, the drive power source is made ON again to restart
the printing operation of the printer. Because normally, the
printer needs a time period to some degree until the printing
operation can be carried out since the drive power source has been
switched on. However, there is a case in which the printer is
intended to be brought into a standby state (awaiting state) by
temporarily stopping to charge the capacitor 15 from the direct
current power source of 5V for saving power or the like. In that
case, when time is taken in charging the capacitor 15 as described
above, there poses a problem that time is taken for recovering the
printer from the standby state to a state of capable of carrying
out printing operation.
SUMMARY OF THE INVENTION
[0007] It is therefore a first object of the present invention to
provide a head driving device capable of saving power by
restraining a power consumption amount of a liquid ejecting
apparatus at standby state.
[0008] Further, it is a second object of the invention to provide a
head driving device capable of recovering to a state for restart
liquid ejecting operation in a short period of time from a standby
state.
[0009] In order to achieve the above object, according to the
present invention, there is provided a head driving device of a
liquid ejecting apparatus, comprising:
[0010] a pressure generating element;
[0011] a bias voltage applying unit which applies a bias voltage to
the pressure generating element;
[0012] a driving voltage generating unit which generates and
outputs a driving voltage to the pressure generating element for
ejecting a liquid droplet from a nozzle of a liquid ejecting head;
and
[0013] a cutoff unit which cuts off the bias voltage applied to the
pressure generating element based on a drive stopping signal.
[0014] Preferably, the bias voltage applying unit is supplied with
a power from a first power source for charging. A voltage of the
first power source is lower than a voltage of a second power source
for supplying a power to the driving voltage generating unit for
charging.
[0015] Preferably, the cutoff unit forms a circuit for discharging
a charge which is charged on the bias voltage applying unit when
the drive stopping signal is outputted.
[0016] Preferably, the cutoff unit forms a circuit for charging the
bias voltage applying unit by supplying the power from the first
power source to the bias voltage applying unit when the drive
stopping signal is not outputted.
[0017] Preferably, the cutoff unit forms a circuit for charging the
bias voltage applying unit by supplying the power from the second
power source to the bias voltage applying unit when the drive
stopping signal is not outputted.
[0018] Preferably, the circuit is formed based on a drive
instruction signal which is outputted when the liquid ejecting head
restarts a liquid ejecting operation from a standby state.
[0019] According to the present invention, there is also provided a
head driving device of a liquid ejecting apparatus, comprising:
[0020] a pressure generating element;
[0021] a bias voltage applying unit which applies a bias voltage to
the pressure generating element;
[0022] a driving voltage generating unit which generates and
outputs a driving voltage to the pressure generating element for
ejecting a liquid droplet from a nozzle of a liquid ejecting
head;
[0023] a first charging unit which charges the bias voltage
applying unit at a first voltage; and
[0024] a second charging unit which charges the bias voltage
applying unit at a second voltage greater than the first voltage
when a drive instruction signal is outputted to the a driving
voltage generating unit.
[0025] Preferably, the second voltage is a voltage outputted from
the driving voltage generating unit.
[0026] Preferably, the drive instruction signal is a signal
outputted when the liquid ejecting head restarts a liquid ejecting
operation from a standby state.
[0027] Preferably, the second charging unit charges the bias
voltage applying unit at a first charge time period shorter than a
second charge time period for charging the bias voltage applying
unit by the first charging unit.
[0028] Preferably, the head driving device further comprising a
cutoff unit which cuts off the bias voltage applied to the pressure
generating element when a drive stopping signal is outputted to the
driving voltage generating unit.
[0029] According to the present invention, there is also provided a
method of cutting-off an applied voltage to a pressure generating
element of a head driving device of a liquid ejecting apparatus,
comprising:
[0030] applying a bias voltage to the pressure generating
element;
[0031] generating and outputting a driving voltage to the pressure
generating element for ejecting a liquid droplet from a nozzle;
and
[0032] cutting-off the bias voltage applied to the pressure
generating element based on a drive stopping signal.
[0033] According to the present invention, there is also provided a
method of charging a bias voltage applying unit for applying a bias
voltage to a pressure generating element of a head driving device
of a liquid ejecting apparatus, comprising:
[0034] applying a bias voltage to the pressure generating
element;
[0035] generating and outputting a driving voltage to the pressure
generating element for ejecting a liquid droplet from a nozzle of a
liquid ejecting head;
[0036] charging the bias voltage applying unit at a first voltage;
and
[0037] charging the bias voltage applying unit at a second voltage
greater than the first voltage when a drive-instruction signal is
outputted to the a driving voltage generating unit.
[0038] According to the invention, there can be provided the head
driving device capable of saving power by restraining a power
consumption amount when the liquid ejecting apparatus is at
standby.
[0039] Further, according to the invention, there can be provided
the head driving device in which liquid ejecting operation is
recovered to a restartable state in a short period of time when the
liquid ejecting apparatus is brought into the standby state.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The above objects and advantages of the present invention
will become more apparent by describing in detail preferred
exemplary embodiments thereof with reference to the accompanying
drawings, wherein:
[0041] FIG. 1 is a circuit constitution diagram of a printing head
driving circuit according to a first embodiment of the
invention;
[0042] FIG. 2 is a timing chart showing a relationship between a
transition of a COM potential and a transition of a bias
potential;
[0043] FIG. 3 is a circuit constitution diagram of a printing head
driving circuit according to a second embodiment of the
invention;
[0044] FIG. 4 is a circuit constitution diagram of a printing head
driving circuit according to a third embodiment of the
invention;
[0045] FIG. 5 is a circuit constitution diagram of a printing head
driving circuit according to a fourth embodiment of the
invention;
[0046] FIG. 6 is a timing chart showing operation of various
portions of the printing head driving circuit illustrated in FIG.
5; and
[0047] FIG. 7 is a circuit constitution diagram of a related
printing head driving circuit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0048] Embodiments of the invention will be explained in details in
reference to the drawings as follows.
[0049] FIG. 1 is a circuit constitution diagram of a printing head
driving circuit according to a first embodiment of the
invention.
[0050] In FIG. 1, a power amplifier 23 constituting a trapezoidal
wave voltage generating circuit 25 along with a D/A converter
(hereinafter, described as "DAC") designated by numeral 21 and a
preamplifier is connected to an analog switch 31 and a
piezoelectric element 33 on a side of a printing head 29 through a
drive voltage transmitting line 27. The power amplifier 23 is
connected to an NPN power transistor 23.sub.1 and a PNP power
transistor 23.sub.2 in push pull connection manner. An output
voltage from a direct current power source of 42V is applied to the
power amplifier 23.
[0051] The trapezoidal wave voltage generating circuit 25 generates
a trapezoidal wave voltage in accordance with a drive instruction
signal outputted from an ASIC (Application Specific Integrated
Circuit) (not illustrated) to the DAC and outputs the trapezoidal
wave voltage to the printing head 29 through the drive voltage
transmitting line 27. The trapezoidal wave voltage generating
circuit 25 stops generating the trapezoidal wave voltage when a
voltage signal of a logical level `L` is outputted from ASIC (not
illustrated) to the DAC as a power save signal.
[0052] On the other hand, the piezoelectric element 33 is connected
with a bias voltage supplying circuit 39 having a resistor 35 and
an (electrolytic) capacitor 37. The bias voltage supplying circuit
39 is connected with a bias voltage controlling circuit 41 for
controlling to charge the capacitor 37 from a direct current power
source of 5V through the resistor 35 and discharge the capacitor 37
to the ground through the resistor 35 based on an instruction
signal (the drive instruction signal or power save signal) from
ASIC (not illustrated). The bias voltage controlling circuit 41 is
provided with a resistor 43, a resistor 45, an NPN transistor
(hereinafter, abbreviated as "TR") 47 (the same as follows)
constituting a cutoff unit, a resistor 49, a resistor 51, a
resistor 53, a PNP transistor (hereinafter, abbreviated as "TR")
55, and TR57 (the same as follows) constituting the cutoff unit
along with TR47. A first switching circuit is constituted by the
resistor 43, the resistor 45, TR47 and the resistor 49, and a
second switching circuit is constituted by the resistor 51, the
resistor 53, TR55 and TR57, respectively.
[0053] In the first switching circuit, the resistor 43 is connected
between a control signal transmitting line 59 connected to, for
example, ASIC (not illustrated) and a base of TR47. The resistor 45
is connected between the base and an emitter of TR47. The resistor
49 is connected between the 5V power source and a collector of the
TR47. The TR47 is brought into a conductive state (turned on) by
applying a voltage signal of a logical level `H` as the drive
instruction signal from the control signal transmitting line 59 to
the base through the resistor 43.
[0054] In the second switch circuit, an emitter side of TR55 is
connected to the direct current power source of 5V, a collector
side thereof is connected to a collector of the TR57 and the
resistor 35 (of the bias voltage supplying circuit 39), and a base
thereof is connected to the resistor 51, respectively. Further, the
collector side of TR57 is connected to the collector of TR55 and
the resistor 35 (of the bias voltage supplying circuit 39), a base
side thereof is connected to the resistor 53 and an emitter side
thereof is connected to the ground. The resistor 51 is connected
between the collector of TR47 (of the first switching circuit) and
the base of TR55. The resistor 53 is connected between the
collector of TR47 (of the first switching circuit) and the base of
TR57. TR55 becomes conductive by making the TR47 (of the first
switching circuit) conductive and becomes nonconductive by making
TR47 nonconductive. On the other hand, TR57 becomes conductive by
making TR47 nonconductive and becomes nonconductive by making TR47
conductive.
[0055] In the constitution, when the drive instruction signal is
outputted from ASIC (not illustrated) to DAC (of the trapezoidal
wave voltage generating circuit 25) in order to execute printing
operation by the printing head 29, thereby, the trapezoidal wave
voltage is started to generate at the trapezoidal wave voltage
generating circuit 25 and the printing head 29 starts printing
operation. As a result, the potential of the drive voltage
transmitting line 27, that is, the COM potential is varied
upward/downward centering on a middle potential (for example, about
20V). On the other hand, the drive instruction signal is also
applied to the bias voltage controlling circuit 41 in synchronism
with application to the DAC. When the drive instruction signal is
applied to the base of TR47 through the resistor 43, TR47 is
conducted and the corrector potential of TR47 becomes substantially
0V and a closed circuit reaching the ground from the 5V power
source through the resistor 49 and TR47 is formed. Thereby, the
base potential of TR55 is lowered down to a voltage value higher
than substantially 0V by an amount of a voltage drop of the
resistor 51 and therefore, TR55 is conducted and the capacitor 37
is charged from the 5V direct current power source through TR55 and
the resistor 35. Here, since the corrector potential of TR47
becomes substantially 0V, TR57 maintains the nonconductive
state.
[0056] Contrary to the above described, when the power save signal
(that is, the voltage signal of the logical level `L`) is outputted
from ASIC (not illustrated) to DAC (of the trapezoidal wave voltage
generating circuit 25) in order to temporarily stop printing
operation by the printing head 29, thereby, the trapezoidal wave
voltage generating circuit 25 stops generating the trapezoidal wave
voltage so that the printing head 29 stops printing operation. As a
result, the COM potential becomes substantially 0V. The power save
signal is applied also to the bias voltage controlling circuit 41
in synchronism with application to the DAC. When the power save
signal is applied to the base of TR47 through the resistor 43, TR47
is switched from a conductive state to an nonconductive state, the
corrector potential of TR47 rises from substantially 0V to a value
constituted by subtracting an amount of the voltage drop of the
resistor 49 from the output voltage (5V) of the direct current
power source. Thereby, TR55 is switched from a conductive state to
an nonconductive state. On the other hand, the base potential of
TR57 rises from substantially 0V up to a value constituted by
subtracting the amount of the voltage drop of the resistor 49 and
an amount of a voltage drop of the resistor 53 from the output
voltage (5V) of the direct current power source of 5V. As a result,
TR57 is switched from an nonconductive state to a conductive state,
a closed circuit reaching the ground from the capacitor 37 through
the resistor 35 and TR57 is formed, charge accumulated-at-the
capacitor 37 is discharged from the capacitor 37 to the ground
through the resistor 35 and TR57. As a result, also the bias
potential becomes substantially 0V. That is, by switching TR47 from
the conductive state to the nonconductive state and switching TR57
from the nonconductive state to the conductive state, when a
driving stop signal is outputted to the drive voltage generating
unit (trapezoidal wave voltage generating circuit 25), in
synchronism with an output of the driving stop signal, the output
of the bias voltage to a nozzle driving unit (piezoelectric element
33) by the bias voltage applying unit ( capacitor 37) is
cutoff.
[0057] FIG. 2 is a timing chart showing a relationship between a
transition of the COM potential and a transition of the bias
potential.
[0058] In FIG. 2, when the power save signal, that is, the voltage
signal at the logical level `L` is outputted from ASIC (not
illustrated) at time t.sub.1, both of the COM potential and the
bias potential are gradually lowered and the both potentials become
substantially 0V at time t.sub.2. At time t.sub.2, there is not a
potential difference between the COM potential and the bias
potential.
[0059] According to the first embodiment of the invention,
stability of printing can be increased and service life of the
piezoelectric element 9 can be prolonged, the potential difference
between the COM potential and the bias potential can be eliminated
and therefore, also the power can be saved by restraining the power
consumption amount of the printer at standby.
[0060] FIG. 3 is a circuit constitution diagram of a printing head
driving circuit according to a second embodiment of the
invention.
[0061] According to the second embodiment, a constitution of a bias
voltage controlling circuit is different from that of the bias
voltage controlling circuit 41 illustrated in FIG. 1 in that the
resistor 43, the resistor 45 and TR47 of the first switching
circuit are removed from the bias voltage controlling circuit 41
shown in FIG. 1, that is, a buffer 61 is provided in place of them,
and further, a PNP transistor is used in place of TR55 of the
second switching circuit, an NPN transistor is used in place of
TR57 to use as TR55' and the cutoff unit, that is, TR57' (the same
as follows). The other constitution is similar to that illustrated
in FIG. 1 and therefore, portions in FIG. 3 the same as those
illustrated in FIG. 1 are attached with the same numerals and an
explanation thereof will be omitted.
[0062] A voltage level of a control signal (drive instruction
signal) transmitted from ASIC (not illustrated) to the trapezoidal
wave voltage generating circuit and a bias voltage controlling
circuit 41' is, for example, 3.3V. The buffer 61 is provided with a
function of converting the voltage level of the control signal from
3.3V to 5V.
[0063] When the drive instruction signal of 3.3V is applied from
the side of ASIC (not illustrated) (to the bias voltage controlling
circuit 41') in the bias voltage controlling circuit 41' having the
aboveescribed constitution, base potentials of TR55', TR57' rise.
Therefore, TR55' is conducted and TR57' is brought into an
nonconductive state. As a result, a closed circuit reaching the
ground from the direct current power source of 5V through TR55',
the resistor 35 and the capacitor 37 and therefore, the capacitor
37 is charged from the direct current power source of 5V. On the
other hand, when the power save signal is applied from the side of
ASIC (not illustrated) (to the bias voltage controlling circuit
41'), thereby, the base potentials of TR55', TR57' are lowered and
therefore, TR57' is conducted and TR55' is brought into an
nonconductive state. As a result, charge accumulated at the
capacitor 37 is discharged through the resistor 35, and TR57'.
[0064] Also in the second embodiment, an effect similar to that in
the first embodiment of the invention can be achieved.
[0065] FIG. 4 is a circuit constitution diagram of a printing head
driving circuit according to a third embodiment of the
invention.
[0066] According to the second embodiment, a constitution of a bias
voltage controlling circuit is different from that of the bias
voltage controlling circuit 41' illustrated in FIG. 3 in that a
Zener diode ZD63 having a Zener voltage (V.sub.z) of, for example,
12V is connected between the ground and a control signal
transmitting line 59' which is connected to a resistor 41 of a
first switching circuit, the resistor 51, the resistor 53 and the
buffer 61 of the second switching circuit respectively, and a
direct current power source connected with the resistor 41 and a
direct current power source connected with TR55' are replaced to
direct current power sources of 42V from the direct current power
sources of 5V. The other constitution is similar to that
illustrated in FIG. 3, and therefore in FIG. 4, portions the same
as those illustrated in FIG. 3 are attached with the same numerals
and an explanation thereof will be omitted.
[0067] In the bias voltage controlling circuit 42 having the
above-described constitution, when the drive instruction signal
(voltage signal at the logical level `H`) is applied from ASIC (not
illustrated) to the bias voltage controlling circuit 42 through the
control signal line 59 in order to recover the printer from the
standby state to the state of capable of executing printing
operation, the base potentials of TR55' and a cutoff unit, that is,
TR57' (the same as follows) rise by an amount of, for example, 5V
from a value constituted by subtracting an amount of the voltage
drop at the resistor 51 from V.sub.2(=12V). Thereby, TR55' is
conducted and TR57' is brought into the nonconductive state. As a
result, a closed circuit reaching the ground from the direct
current power source of 42V through TR55', the resistor 35 and the
capacitor 37 is formed and therefore, the capacitor 37 is charged
from the direct current power source of 42V by a direct current
voltage of, for example, about 11V (by voltage drop at the resistor
35). In this case, the supply voltage is switched to the direct
current voltage of 42V from the direct current voltage of 5V and
therefore, even when a capacitance of the capacitor 37 is as larger
as, for example, 4000 .mu.F, the voltage of charging the capacitor
37 reaches a predetermined value (for example, 5V) in a
comparatively short period of time.
[0068] FIG. 5 is a circuit constitution diagram of a printing head
driving circuit according to a fourth embodiment of the
invention.
[0069] According to the fourth embodiment, a constitution of the
printing head driving circuit is different from that of the
printing head driving circuit illustrated in FIG. 5 in that a
control signal transmitting line 65, a second charging unit, that
is, a charge controlling circuit 67 (same as follows), a
semiconductor switching element 69, and a rapid charging line 71
are added to the portions of the printing head driving circuit
illustrated in FIG. 1. Here, the bias voltage controlling circuit
41 serves as a first charging unit.
[0070] The rapid charging line 71 connects an output side of the
power amplifier 23 and the (electrolytic) capacitor 37, and the
rapid charging line 71 is connected with the semiconductor
switching element 69. The semiconductor switching element 69 is
operated to be made ON/OFF by a charge control signal applied from
the charge controlling circuit 67. By operating to make the
semiconductor switching element 69 ON, the trapezoidal wave voltage
outputted through-the power amplifier 23 is supplied to the
(electrolytic) capacitor 37 through the rapid charging line 71.
Further, the control signal transmitting line 65 connects ASIC (not
illustrated) and the charge controlling circuit 67 independently
from the control signal transmitting line 59. The charge
controlling circuit 67 outputs the charge control signal to the
semiconductor switching element 69 in accordance with the
instruction signal transmitted from ASIC (not illustrated) through
the control signal transmitting line 65.
[0071] In the above configuration, the operation for printing of
the printing head 29 of this fourth embodiment is substantially
same as that of the first embodiment. However, when the printer
brought into the standby state (awaiting state) by temporally
stopping to charge the (electrolytic) capacitor 37 from the direct
current power source of 5V for saving power or the like is
recovered to a state of capable of carrying out the printing
operation, the drive instruction signal (voltage signal at the
logical level `H`) is applied from ASIC (not illustrated) to DAC
and the bias voltage controlling circuit 41 through the control
signal line 59, also the drive instruction signal is applied to the
charge controlling circuit 67 through the control signal
transmitting line 65. Thereby, the capacitor 37 is charged from the
direct current power source of 5V through the bias voltage
controlling circuit 41 and the resistor 35 and the capacitor 37 is
charged from the direct current power source of 42V through the
power amplifier 23 and the rapid charging line 71 by operating to
make the semiconductor switching element 69 ON by the charge
control signal from the charge controlling circuit 67.
[0072] The capacitor 37 is stopped from being charged through the
rapid charging line 71. This stopping of the charge is separate
from an outputting of the power save signal (voltage signal at the
logical level `L`) from ASIC (not illustrated) to the side of the
trapezoidal wave voltage generating circuit through the control
signal transmitting line 59. That is, a stopping of the charging
operation through the rapid charging line 71 is based on a charge
stop control signal applied to the charge controlling circuit 67
through the control signal transmitting line 65 from ASIC (not
illustrated). The semiconductor switching element 69 is turned OFF
to stop the charging operation in accordance with the charge stop
instruction signal applied from the charge controlling circuit 67
to the semiconductor switching element 69.
[0073] FIG. 6 is a timing chart showing operation of respective
portions of the printing head driving circuit illustrated in FIG.
5.
[0074] In FIG. 6, at time T.sub.1, when a drive instruction signal
81 is outputted from ASIC (not illustrated) to the trapezoidal wave
voltage generating circuit and the bias voltage controlling circuit
41 respectively and further a charge control signal 85 is outputted
(ON) from ASIC (not illustrated) to the charge controlling circuit
67, a COM potential 83 rises from 0V to a predetermined potential
with a constant inclination. On the other hand, a charge voltage 87
of the capacitor 37 temporarily exceeds 5V at previously programmed
predetermined time T2 by charging from the direct current power
source of 5V through the bias voltage controlling circuit 41 and
charging in the trapezoidal waveform from DAC through the power
amplifier 23 and the rapid charging line 71 and thereafter becomes
5V constituting predetermined rise of voltage at time T3.
[0075] At time T3, the charge control signal 85 is made OFF
(logical level becomes `L`). At time T3 and thereafter, the charge
control signal 85 is not made ON again. Next at time T4, T5, T6,
and T7, the COM potential is varied upward and downward in
accordance with a value of the trapezoidal wave voltage outputted
from the trapezoidal wave voltage generating circuit. Further, at
T8, when the power save signal (logical level `L`) is outputted
from ASIC (not illustrated) to the trapezoidal wave voltage
generating circuit and the bias voltage controlling circuit 41, the
COM potential immediately becomes 0V and the charge voltage of the
capacitor 37 becomes 0V at time T9 after elapse of a predetermined
time period from time T8.
[0076] Although the preferable embodiments of the invention have
been explained, the embodiments are only exemplifications for
explaining the invention and do not limit the scope of the
invention only to the embodiments. The invention can be embodied
also in other various modes for carrying out the invention.
* * * * *